ART. XXVI.-Diluvial Strix on Fragments in Situ; by O. N. STODDARD, Prof. Nat. Science, Miami University.

WHILE examining a few days since the fossils and the striæ pertaining to the Silurian formation of this vicinity, I discovered gravel, small boulders, and fragments of the underlying rock, very much worn by diluvial agencies and manifestly now lying where they were when striated. They were nearly uncovered some three years since in forming a bed for a railroad; the remaining denudation has been accomplished by the action of the rains upon the unfinished and unprotected bed.

They have been exposed along the road for about fifteen feet, and across nearly the whole breadth. At one point the material was a mass of gravel closely packed, and covering several square feet; at other places fragments of Silurian limestone, mingled promiscuously with small boulders of granite, greenstone, hornblende and quartz, the whole embedded in compact clay. The striated surfaces were in the same plane, and at one point the underlying rock was exposed, also striated. The direction of the grooves varied from 5° to 8° south of east.

No one, I presume, will for a moment entertain the idea, that the one hundred and forty-one pieces composing this bed were transported to this spot, having been striated elsewhere, and accidentally deposited with their surfaces in the same plane, and their grooves substantially parallel. The chances against such an occurrence are so enormous, that we might with safety say, it could not happen except by miracle.

The bearing of this example upon the different theories of diluvial action is obvious. The agency of running water may be dismissed as utterly inadequate to explain the facts in question. Icebergs driven onward by the waves and currents of a paleozoic sea afford a solution but little more plausible. Icebergs might plough up the bottom and scatter the fragments, but could not retain them in place and striate them. It seems necessary to admit that they were firmly frozen into the clay and thus held in position, while some overlying mass slowly ground off their exposed surfaces. If we admit that the bed was frozen during the striating process, then must we also admit. that it could not have been covered at that time by any considerable depth of water. It is hardly necessary to state to a geologist, that no known agency so admirably meets all the conditions of this case, and no supposition so satisfies the mind as this, that glaciers once overspread this region, holding the beds underneath frost-bound; and, while their enormous pressure downwards, prevented displacement in an upward direction, their motion towards the south, ground down, not only the rocks in

place, but also these fragments, almost as firmly fixed by frost as the rocks themselves. On examination, a few of the pieces were found to be grooved on the under surface also. In one or two cases the stria on opposite sides were nearly parallel, but generally inclined at a considerable angle.

Probably these fragments were at first embedded in the glacier and received, while in that position, the scratches on their under surface, but were subsequently detached from the glacier, embedded and frozen in the clay, where they were reduced to the condition in which they were found.

It may not be amiss to remark in conclusion, that striæ are abundant upon the surface rocks of this region, their direction varying from 1° to 11° east of south. The most durable boulders generally exhibit upon one or more of their surfaces distinct traces of the same abrading agency.

Miami University, June 11th, 1859.

ART. XXVII.-Vibrations in the Waterfall at Holyoke, Mass.; by Prof. E. S. SNELL, Amherst College.

AT the meeting of the American Scientific Association held in Montreal, August, 1857, I read a paper on the vibrations of the fall at Holyoke, in which I attributed the movement to the rarefaction of air in the tube behind the sheet, this rarefaction being caused by the action of the water, which carries down the adjacent air, and throws it up in foam mostly on the outside of the fall. In that paper I described two modes of vibration which I had observed, that agreed well with the supposition of acoustic pulsations in a tube of air 1008 feet long, and having two nodal sections in one case, and four in the other. I also stated my impression that I had, many years before, noticed a much slower rate of vibration, which accorded equally well with the existence of one nodal section in the tube.

Since the reading of the above-mentioned paper, I have observed the condition of the fall at four different times. In October and November, 1857, I noticed the same rates of vibration very nearly, which I had previously reported. But on the 16th of April, 1859, I found the water four or five feet deep on the edge of the dam, the temperature of the air about 45°, and the number of oscillations only eighty-two per minute. Again, on the 25th of July last, I found the water lower than I had seen it before, (less than three inches deep,) and no vibrations, either in the sheet, or the air at the end of the cavity behind it.

There are, therefore, at least three very different rates of vibration in this fall, the slowest when the depth of water is greatest,

and the most rapid when it is about one foot deep, the vibrations ceasing altogether when the depth is so small as three inches. In the following tabular statement, the four first columns show at once the facts as they stand connected in the few observations which I have made, and the last column contains the numbers calculated for an open tube 1008 feet long, with four nodes for the third and fourth observations, two nodes for the first, second, and fifth, and one node for the sixth.

I used the formula in Peirce's Treatise on Sound, N=n

where N is the number of vibrations, n the number of nodes, V the velocity of sound, and L the length of the tube. It is observable, that the calculated rates are higher than the observed, in the cases of most rapid vibration, and lower, in those of least rapidity, while in the medium rates, they very closely agree. As to the seventh case, the sheet was so thin, that it was divided into filaments and broken into spray, and the air had free ingress and egress through its whole length; the acoustic tube being thus destroyed, no vibrations could be produced.

Notwithstanding the discrepancies between the numbers in the two last columns, I think the general correspondence between them points to the true nature of the cause, especially when taken in connection with the fact, that the pulsations are noticeable only in the water and in the air,-not at all in the dam itself, nor in the rock or soil immediately adjacent. It must be remembered also, that the pitch of musical pipes does not fully conform to the formulæ, but varies with the breadth of opening and the mode of exciting vibrations.

This seems to be one of the numerous cases, in which the body which excites vibrations in another, is itself thrown into synchronous vibration by reaction, and then, by its own inertia or elasticity, controls the common rate of both. The sheet of water in its descent first produces rarefaction of the enclosed air by removing a part of it. The immediate effect is a collapse of the sheet of water, as well as a rush of air in at the ends. But the inertia of a thick mass of water will prevent its recovering its natural position so soon as if it were thinner; hence, the aircolumn divides itself into such a number of segments, that the water and the air can adjust their movements to each other.

In a manner somewhat like this, a stream of air from the lips, driven across the embouchure of a flute, excites vibrations in the column of air, with such frequency that it can itself vibrate in unison with it. But, if the stream is blown more and more swiftly, its elasticity will at length be too great for so slow a rate, and then the column will divide into shorter segments, and the two will continue their vibrations harmoniously upon a higher key. A skillful player can in this way by his mere breath produce six or eight harmonic notes on the flute, when all the holes are closed.

At the time when I witnessed the comparatively slow oscillation of 82 per minute, I was surprised by the great strength of the current of air, as it rushed into the opening at the end of the dam. I could not venture within the passage through the pier, lest I should be swept in behind the sheet; nor could I stand at the entrance of the arch, without bracing myself, by placing both hands on the corners. There was, however, no alternate outward blast, but only a lull, or cessation of all motion; which shows, that the excess of air that pours in at every pulse, is carried out again in some other way; and there is no conceivable way for it to escape, except to be driven down by the falling water, and poured up externally in a bed of foam. It had never occurred to me before, that the velocity of the air-current must be greater, the longer the interval between the pulses, since the rarefaction within the tube will be greater nearly in the ratio of the same interval.

In September, 1857, a paper was read before the Boston Society of Natural History, in which objections were made to my view of the source of the vibrations, and the cause assigned for them was the impulse on the rock produced by successive swells of the sheet, extending parallel to the edge of the dam, from one side of the river to the other. If this is the cause, then the vibrations are first excited in the rock, and communicated thence to the air. But the rock and soil in the immediate vicinity of the Holyoke fall are not perceived to move in the least, while the air sways a loose garment back and forth three or four inches, keeping time with the visible and audible pulsations of the sheet of water, and at the end of the tube sometimes rushes so violently, that a man can scarcely stand against it. That alternate swells and contractions cannot exist in a falling sheet of water, and if so, that they cannot cause sensible undulations in the earth, I am not prepared to assert; but I believe that any unbiased observer will find it quite absurd to apply such an explanation to the strong puffing of the air which is usually so noticeable at the Holyoke fall.

ART. XXVIII.-Caricography; by Prof. C. DEWEY.

(Continued from vol. xxiv, p. 48, Second Series.)

No. 254. C. alata, Tor. Mon.

Spica composita; spiculis 5-8, ovalibus, sessilibus, crassis, superne aggregatis, densifloris, infirne staminiferis; fructibus suborbiculatis, interdum obovatis, distigmaticis, subplanis, abrupti brevi-rostratis, bidentatis, lato-alatis, rostro subscabris, squama ovato-lanceolata brevioribus.

Culm 3-4 feet high, smooth, with rough edged leaves; pale green; stigmas two. North Carolina and Georgia-Torrey ; Florida-Chapman; a pine sedge-grass.

255. C. striata, Mx. Boott, Illust., No. 141.

Spicis staminiferis, 1-4, sæpe 2, oblongis, cylindraceis, erectis, subrubris, inferioribus sessilibus et brevioribus; pistilliferis 2, raro 1, oblongo-cylindraceis, erectis, bracteatis, densi-floris, suprema sæpe apice staminifera, tristigmaticis; fructibus ovatis acuminatis sub-inflatis brevi-rostratis scabro-pubescentibus nervosis ore bifidis, squama ovata acuta fusca vel sub-rubra albi-marginata duplo longioribus.

Culm 1-2 feet high, erect, stiff, leafy-bracteate, longer than the striate and lanceolate leaves, reddish at the root.

Penn. Muhlenberg; New Jersey-Torrey and also Knierskern; Florida-Chapman.

Confounded with C. polymorpha, Muh.; but Dr. Boott found the Florida plant, fully like the others, to be C. striata in the Herbarium of Micheaux. This discovery makes a change in its designation: it led also to the other changes. Thus,

2

C. Halseyana, vol. xi, p. 313, of this Journal, becomes var. of C. polymorpha, Muh. Gram. p. 239. Boott, Illust., No. 56. If this change should prove untenable, the original name can be restored. Years after C. Hals yana was named, I found it with different forms, named polymorpha in Muhl, herbarium.

256. C. utriculata. Boott. Illust., No. 37.

Spicis staminiferis 3-4, cylindraceis, erectis, gracilibus; pistilliferis 2-4, sæpe 3, longo-cylindraceis magnis subremotis, sæpe apice staminiferis, sessillibus, longo-foliaceo-bracteatis, infirma inferne attenuata et laxiflora et sub-pedunculata fructibus tristigmaticis ovati-oblongis vel ovata ellipsoides, cum rostro terati et bifurcato, glabris, subinflatis, stramineis, revorsis, squama lanceolata purpurea, angusta scabro-aristata longioribus.